Vagus nerve and carotid baroreceptor stimulation system

ABSTRACT

Systems and methods are provided for delivering vagus nerve stimulation and carotid baroreceptor stimulation to patients for treating chronic heart failure and hypertension. The vagus nerve stimulation and carotid baroreceptor stimulation therapies may be provided using a single implantable pulse generator, which can coordinate delivery of the therapies.

FIELD

This application relates to stimulation therapies.

BACKGROUND

Chronic heart failure (CHF) and other forms of chronic cardiac dysfunction (CCD) may be related to an autonomic imbalance of the sympathetic and parasympathetic nervous systems that, if left untreated, can lead to cardiac arrhythmogenesis, progressively worsening cardiac function and eventual patient death. CHF is pathologically characterized by an elevated neuroexitatory state and is accompanied by physiological indications of impaired arterial and cardiopulmonary baroreflex function with reduced vagal activity.

CHF triggers compensatory activations of the sympathoadrenal (sympathetic) nervous system and the renin-angiotensin-aldosterone hormonal system, which initially helps to compensate for deteriorating heart-pumping function, yet, over time, can promote progressive left ventricular dysfunction and deleterious cardiac remodeling. Patients suffering from CHF are at increased risk of tachyarrhythmias, such as atrial fibrillation (AF), ventricular tachyarrhythmias (ventricular tachycardia (VT) and ventricular fibrillation (VF)), and atrial flutter, particularly when the underlying morbidity is a form of coronary artery disease, cardiomyopathy, mitral valve prolapse, or other valvular heart disease. Sympathoadrenal activation also significantly increases the risk and severity of tachyarrhythmias due to neuronal action of the sympathetic nerve fibers in, on, or around the heart and through the release of epinephrine (adrenaline), which can exacerbate an already-elevated heart rate.

The standard of care for managing CCD in general continues to evolve. For instance, new therapeutic approaches that employ electrical stimulation of neural structures that directly address the underlying cardiac autonomic nervous system imbalance and dysregulation have been proposed. In one form, controlled stimulation of the cervical vagus nerve beneficially modulates cardiovascular regulatory function. Vagus nerve stimulation (VNS) has been used for the clinical treatment of drug-refractory epilepsy and depression, and more recently has been proposed as a therapeutic treatment of heart conditions such as CHF. For instance, VNS has been demonstrated in canine studies as efficacious in simulated treatment of AF and heart failure, such as described in Zhang et al., “Chronic Vagus Nerve Stimulation Improves Autonomic Control and Attenuates Systemic Inflammation and Heart Failure Progression in a Canine High-Rate Pacing Model,” Circ Heart Fail 2009, 2, pp. 692-699 (Sep. 22, 2009), the disclosure of which is incorporated by reference. The results of a multi-center open-label phase II study in which chronic VNS was utilized for CHF patients with severe systolic dysfunction is described in De Ferrari et al., “Chronic Vagus Nerve Stimulation: A New and Promising Therapeutic Approach for Chronic Heart Failure,” European Heart Journal, 32, pp. 847-855 (Oct. 28, 2010).

VNS therapy commonly requires implantation of a neurostimulator, a surgical procedure requiring several weeks of recovery before the neurostimulator can be activated and a patient can start receiving VNS therapy. Even after the recovery and activation of the neurostimulator, a full therapeutic dose of VNS is not immediately delivered to the patient to avoid causing significant patient discomfort and other undesirable side effects. Instead, to allow the patient to adjust to the VNS therapy, a titration process is utilized in which the intensity is gradually increased over a period of time under a control of a physician, with the patient given time between successive increases in VNS therapy intensity to adapt to the new intensity. As stimulation is chronically applied at each new intensity level, the patient's tolerance threshold, or tolerance zone boundary, gradually increases, allowing for an increase in intensity during subsequent titration sessions. The titration process can take significantly longer in practice because the increase in intensity is generally performed by a physician or other healthcare provider, and thus, for every step in the titration process to take place, the patient has to visit the provider's office to have the titration performed. Scheduling conflicts in the provider's office may increase the time between titration sessions, thereby extending the overall titration process, during which the patient in need of VNS does not receive the VNS at the full therapeutic intensity.

CHF patients frequently also suffer from hypertension. The use of implantable systems for electrically stimulating the carotid sinus has been proposed for the treatment of hypertension. These systems utilize a pulse generator implanted subcutaneously near the collarbone and carotid sinus leads placed on the carotid arteries to deliver stimulation to the carotid baroreceptors. The use of these systems has also been proposed for promoting the reversal of ventricular remodeling in subjects with advanced heart failure.

Accordingly, there is a need remains for improved treatment methods utilizing stimulation therapies for treating chronic cardiac dysfunction and other conditions.

SUMMARY

Systems and methods are provided for delivering vagus nerve stimulation and carotid baroreceptor stimulation to patients for treating chronic heart failure and hypertension. The vagus nerve stimulation and carotid baroreceptor stimulation therapies may be provided using a single implantable pulse generator, which can coordinate delivery of the therapies to modify the stimulation parameters based on a variety of factors.

In accordance with embodiments of the present invention, an implantable neurostimulation system is provided, comprising: a pulse generation module comprising a control system, a vagus nerve stimulation (VNS) subsystem, and an implantable carotid baroreceptor stimulation (CBS) subsystem; a first VNS electrode assembly coupled to the pulse generation module, said first VNS electrode assembly configured to couple to and deliver electrical stimulation to a vagus nerve; and a first CBS electrode assembly coupled to the pulse generation module, said first CBS electrode assembly configured to couple to and deliver electrical stimulation to carotid baroreceptors. In accordance with some embodiments, the control system is configured to modify a stimulation parameter of the CBS subsystem in response to detected state changes.

In accordance with embodiments of the present invention, a method of operating an implantable neurostimulation system is provided, comprising: delivering a vagus nerve stimulation (VNS) therapy to a vagus nerve with a VNS subsystem of a pulse generation module; and delivering a carotid baroreceptor stimulation (CBS) therapy to carotid baroreceptors with a CBS subsystem of the pulse generation module.

In accordance with embodiments of the present invention, a method of operating an implantable stimulation system is provided, comprising: implanting a pulse generation module in a chest of a patient; tunneling a lead assembly between a neck of the patient and the pulse generation module, said lead assembly comprising a first electrode assembly, a second electrode assembly, and a proximal connector; through a single incision in the neck of the patient, coupling the first electrode assembly to a carotid artery and coupling the second electrode assembly to a vagus nerve; and coupling the proximal connector to the pulse generation module.

Still other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein are described embodiments by way of illustrating the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and the scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front anatomical diagram showing, by way of example, placement of an implantable vagus stimulation device in a male patient, in accordance with one embodiment.

FIGS. 2A and 2B are diagrams respectively showing the implantable neurostimulator and the simulation therapy lead of FIG. 1.

FIG. 3 is a diagram showing an external programmer for use with the implantable neurostimulator of FIG. 1.

FIG. 4 is a diagram showing electrodes provided as on the stimulation therapy lead of FIG. 2 in place on a vagus nerve in situ.

FIG. 5 is a graph showing, by way of example, the relationship between the targeted therapeutic efficacy and the extent of potential side effects resulting from use of the implantable neurostimulator of FIG. 1.

FIG. 6 is a graph showing, by way of example, the optimal duty cycle range based on the intersection depicted in FIG. 3.

FIG. 7 is a timing diagram showing, by way of example, a stimulation cycle and an inhibition cycle of VNS as provided by implantable neurostimulator of FIG. 1.

FIGS. 8A-8C are illustrative charts reflecting a heart rate response to gradually increased stimulation intensity at different frequencies.

FIGS. 9A-9G illustrate front anatomical diagrams showing various configurations of CBS/VNS systems, in accordance with embodiments of the present invention.

FIG. 10 illustrates a block diagram of an implantable pulse generation module, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

CHF and other cardiovascular diseases cause derangement of autonomic control of the cardiovascular system, favoring increased sympathetic and decreased parasympathetic central outflow. These changes are accompanied by elevation of basal heart rate arising from chronic sympathetic hyperactivation along the neurocardiac axis.

The vagus nerve is a diverse nerve trunk that contains both sympathetic and parasympathetic fibers, and both afferent and efferent fibers. These fibers have different diameters and myelination, and subsequently have different activation thresholds. This results in a graded response as intensity is increased. Low intensity stimulation results in a progressively greater tachycardia, which then diminishes and is replaced with a progressively greater bradycardia response as intensity is further increased. Peripheral neurostimulation therapies that target the fluctuations of the autonomic nervous system have been shown to improve clinical outcomes in some patients. Specifically, autonomic regulation therapy results in simultaneous creation and propagation of efferent and afferent action potentials within nerve fibers comprising the cervical vagus nerve. The therapy directly improves autonomic balance by engaging both medullary and cardiovascular reflex control components of the autonomic nervous system. Upon stimulation of the cervical vagus nerve, action potentials propagate away from the stimulation site in two directions, efferently toward the heart and afferently toward the brain. Efferent action potentials influence the intrinsic cardiac nervous system and the heart and other organ systems, while afferent action potentials influence central elements of the nervous system.

An implantable vagus nerve stimulator, such as used to treat drug-refractory epilepsy and depression, can be adapted for use in managing chronic cardiac dysfunction (CCD) through therapeutic bi-directional vagus nerve stimulation. FIG. 1 is a front anatomical diagram showing, by way of example, placement of an implantable medical device (e.g., a vagus nerve stimulation (VNS) system 11, as shown in FIG. 1) in a male patient 10, in accordance with embodiments of the present invention. The VNS provided through the stimulation system 11 operates under several mechanisms of action. These mechanisms include increasing parasympathetic outflow and inhibiting sympathetic effects by inhibiting norepinephrine release and adrenergic receptor activation. More importantly, VNS triggers the release of the endogenous neurotransmitter acetylcholine and other peptidergic substances into the synaptic cleft, which has several beneficial anti-arrhythmic, anti-apoptotic, and anti-inflammatory effects as well as beneficial effects at the level of the central nervous system.

The implantable vagus stimulation system 11 comprises an implantable neurostimulator or pulse generator 12 and a stimulating nerve electrode assembly 125. The stimulating nerve electrode assembly 125, preferably comprising at least an electrode pair, is conductively connected to the distal end of an insulated, electrically conductive lead assembly 13 and electrodes 14. The electrodes 14 may be provided in a variety of forms, such as, e.g., helical electrodes, probe electrodes, cuff electrodes, as well as other types of electrodes.

The implantable vagus stimulation system 11 can be remotely accessed following implant through an external programmer, such as the programmer 40 shown in FIG. 3 and described in further detail below. The programmer 40 can be used by healthcare professionals to check and program the neurostimulator 12 after implantation in the patient 10 and to adjust stimulation parameters during the initial stimulation titration process. In some embodiments, an external magnet may provide basic controls, such as described in commonly assigned U.S. Pat. No. 8,600,505, entitled “Implantable Device For Facilitating Control Of Electrical Stimulation Of Cervical Vagus Nerves For Treatment Of Chronic Cardiac Dysfunction,” the disclosure of which is incorporated by reference. For further example, an electromagnetic controller may enable the patient 10 or healthcare professional to interact with the implanted neurostimulator 12 to exercise increased control over therapy delivery and suspension, such as described in commonly-assigned U.S. Pat. No. 8,571,654, entitled “Vagus Nerve Neurostimulator With Multiple Patient-Selectable Modes For Treating Chronic Cardiac Dysfunction,” the disclosure of which is incorporated by reference. For further example, an external programmer may communicate with the neurostimulation system 11 via other wired or wireless communication methods, such as, e.g., wireless RF transmission. Together, the implantable vagus stimulation system 11 and one or more of the external components form a VNS therapeutic delivery system.

The neurostimulator 12 is typically implanted in the patient's right or left pectoral region generally on the same side (ipsilateral) as the vagus nerve 15, 16 to be stimulated, although other neurostimulator-vagus nerve configurations, including contra-lateral and bi-lateral are possible. A vagus nerve typically comprises two branches that extend from the brain stem respectively down the left side and right side of the patient, as seen in FIG. 1. The electrodes 14 are generally implanted on the vagus nerve 15, 16 about halfway between the clavicle 19 a-b and the mastoid process. The electrodes may be implanted on either the left or right side. The lead assembly 13 and electrodes 14 are implanted by first exposing the carotid sheath and chosen branch of the vagus nerve 15, 16 through a latero-cervical incision (perpendicular to the long axis of the spine) on the ipsilateral side of the patient's neck 18. The helical electrodes 14 are then placed onto the exposed nerve sheath and tethered. A subcutaneous tunnel is formed between the respective implantation sites of the neurostimulator 12 and helical electrodes 14, through which the lead assembly 13 is guided to the neurostimulator 12 and securely connected.

In one embodiment, the neural stimulation is provided as a low level maintenance dose independent of cardiac cycle. The stimulation system 11 bi-directionally stimulates either the left vagus nerve 15 or the right vagus nerve 16. However, it is contemplated that multiple electrodes 14 and multiple leads 13 could be utilized to stimulate simultaneously, alternatively or in other various combinations. Stimulation may be through multimodal application of continuously-cycling, intermittent and periodic electrical stimuli, which are parametrically defined through stored stimulation parameters and timing cycles. Both sympathetic and parasympathetic nerve fibers in the vagosympathetic complex are stimulated. A study of the relationship between cardiac autonomic nerve activity and blood pressure changes in ambulatory dogs is described in J. Hellyer et al., “Autonomic Nerve Activity and Blood Pressure in Ambulatory Dogs,” Heart Rhythm, Vol. 11(2), pp. 307-313 (February 2014). Generally, cervical vagus nerve stimulation results in propagation of action potentials from the site of stimulation in a bi-directional manner. The application of bi-directional propagation in both afferent and efferent directions of action potentials within neuronal fibers comprising the cervical vagus nerve improves cardiac autonomic balance. Afferent action potentials propagate toward the parasympathetic nervous system's origin in the medulla in the nucleus ambiguus, nucleus tractus solitarius, and the dorsal motor nucleus, as well as towards the sympathetic nervous system's origin in the intermediolateral cell column of the spinal cord. Efferent action potentials propagate toward the heart 17 to activate the components of the heart's intrinsic nervous system. Either the left or right vagus nerve 15, 16 can be stimulated by the stimulation system 11. The right vagus nerve 16 has a moderately lower (approximately 30%) stimulation threshold than the left vagus nerve 15 for heart rate effects at the same stimulation frequency and pulse width.

The VNS therapy is delivered autonomously to the patient's vagus nerve 15, 16 through three implanted components that include a neurostimulator 12, lead assembly 13, and electrodes 14. FIGS. 2A and 2B are diagrams respectively showing the implantable neurostimulator 12 and the stimulation lead assembly 13 of FIG. 1. In one embodiment, the neurostimulator 12 can be adapted from a VNS Therapy Demipulse Model 103 or AspireSR Model 106 pulse generator, manufactured and sold by Cyberonics, Inc., Houston, Tex., although other manufactures and types of implantable VNS neurostimulators could also be used. The stimulation lead assembly 13 and electrodes 14 are generally fabricated as a combined assembly and can be adapted from a Model 302 lead, PerenniaDURA Model 303 lead, or PerenniaFLEX Model 304 lead, also manufactured and sold by Cyberonics, Inc., in two sizes based, for example, on a helical electrode inner diameter, although other manufactures and types of single-pin receptacle-compatible therapy leads and electrodes could also be used.

Referring first to FIG. 2A, the system 20 may be configured to provide multimodal vagus nerve stimulation. In a maintenance mode, the neurostimulator 12 is parametrically programmed to deliver continuously-cycling, intermittent and periodic ON-OFF cycles of VNS. Such delivery produces action potentials in the underlying nerves that propagate bi-directionally, both afferently and efferently.

The neurostimulator 12 includes an electrical pulse generator that is tuned to improve autonomic regulatory function by triggering action potentials that propagate both afferently and efferently within the vagus nerve 15, 16. The neurostimulator 12 is enclosed in a hermetically sealed housing 21 constructed of a biocompatible material, such as titanium. The housing 21 contains electronic circuitry 22 powered by a battery 23, such as a lithium carbon monofluoride primary battery or a rechargeable secondary cell battery. The electronic circuitry 22 may be implemented using complementary metal oxide semiconductor integrated circuits that include a microprocessor controller that executes a control program according to stored stimulation parameters and timing cycles; a voltage regulator that regulates system power; logic and control circuitry, including a recordable memory 29 within which the stimulation parameters are stored, that controls overall pulse generator function, receives and implements programming commands from the external programmer, or other external source, collects and stores telemetry information, processes sensory input, and controls scheduled and sensory-based therapy outputs; a transceiver that remotely communicates with the external programmer using radio frequency signals; an antenna, which receives programming instructions and transmits the telemetry information to the external programmer; and a reed switch 30 that provides remote access to the operation of the neurostimulator 12 using an external programmer, a simple patient magnet, or an electromagnetic controller. The recordable memory 29 can include both volatile (dynamic) and non-volatile/persistent (static) forms of memory, such as firmware within which the stimulation parameters and timing cycles can be stored. Other electronic circuitry and components are possible.

The neurostimulator 12 includes a header 24 to securely receive and connect to the lead assembly 13. In one embodiment, the header 24 encloses a receptacle 25 into which a single pin for the lead assembly 13 can be received, although two or more receptacles could also be provided, along with the corresponding electronic circuitry 22. The header 24 internally includes a lead connector block (not shown) and a set of screws 26.

In some embodiments, the housing 21 may also contain a heart rate sensor 31 that is electrically interfaced with the logic and control circuitry, which receives the patient's sensed heart rate as sensory inputs. The heart rate sensor 31 monitors heart rate using an ECG-type electrode. Through the electrode, the patient's heart beat can be sensed by detecting ventricular depolarization. In a further embodiment, a plurality of electrodes can be used to sense voltage differentials between electrode pairs, which can undergo signal processing for cardiac physiological measures, for instance, detection of the P-wave, QRS complex, and T-wave. The heart rate sensor 31 provides the sensed heart rate to the control and logic circuitry as sensory inputs that can be used to determine the onset or presence of arrhythmias, particularly VT, and/or to monitor and record changes in the patient's heart rate over time or in response to applied stimulation signals.

Referring next to FIG. 2B, the lead assembly 13 delivers an electrical signal from the neurostimulator 12 to the vagus nerve 15, 16 via the electrodes 14. On a proximal end, the lead assembly 13 has a lead connector 27 that transitions an insulated electrical lead body to a metal connector pin 28. During implantation, the connector pin 28 is guided through the receptacle 25 into the header 24 and securely fastened in place using the set screws 26 to electrically couple the lead assembly 13 to the neurostimulator 12. On a distal end, the lead assembly 13 terminates with the electrode 14, which bifurcates into a pair of anodic and cathodic electrodes 62 (as further described infra with reference to FIG. 4). In one embodiment, the lead connector 27 is manufactured using silicone and the connector pin 28 is made of stainless steel, although other suitable materials could be used, as well. The insulated lead body 13 utilizes a silicone-insulated alloy conductor material.

In some embodiments, the electrodes 14 are helical and placed around the cervical vagus nerve 15, 16 at the location below where the superior and inferior cardiac branches separate from the cervical vagus nerve. In alternative embodiments, the helical electrodes may be placed at a location above where one or both of the superior and inferior cardiac branches separate from the cervical vagus nerve. In one embodiment, the helical electrodes 14 are positioned around the patient's vagus nerve oriented with the end of the helical electrodes 14 facing the patient's head. In an alternate embodiment, the helical electrodes 14 are positioned around the patient's vagus nerve 15, 16 oriented with the end of the helical electrodes 14 facing the patient's heart 17. At the distal end, the insulated electrical lead body 13 is bifurcated into a pair of lead bodies that are connected to a pair of electrodes. The polarity of the electrodes could be configured into a monopolar cathode, a proximal anode and a distal cathode, or a proximal cathode and a distal anode.

The neurostimulator 12 may be interrogated prior to implantation and throughout the therapeutic period with a healthcare provider-operable control system comprising an external programmer and programming wand (shown in FIG. 3) for checking proper operation, downloading recorded data, diagnosing problems, and programming operational parameters, such as described in commonly-assigned U.S. Pat. Nos. 8,600,505 and 8,571,654, cited supra. FIG. 3 is a diagram showing an external programmer 40 for use with the implantable neurostimulator 12 of FIG. 1. The external programmer 40 includes a healthcare provider operable programming computer 41 and a programming wand 42. Generally, use of the external programmer is restricted to healthcare providers, while more limited manual control is provided to the patient through “magnet mode.”

In one embodiment, the external programmer 40 executes application software 45 specifically designed to interrogate the neurostimulator 12. The programming computer 41 interfaces to the programming wand 42 through a wired or wireless data connection. The programming wand 42 can be adapted from a Model 201 Programming Wand, manufactured and sold by Cyberonics, Inc., and the application software 45 can be adapted from the Model 250 Programming Software suite, licensed by Cyberonics, Inc. Other configurations and combinations of external programmer 40, programming wand 42 and application software 45 are possible.

The programming computer 41 can be implemented using a general purpose programmable computer and can be a personal computer, laptop computer, ultrabook computer, netbook computer, handheld computer, tablet computer, smart phone, or other form of computational device. In one embodiment, the programming computer is a tablet computer that may operate under the iOS operating system from Apple Inc., such as the iPad from Apple Inc., or may operate under the Android operating system from Google Inc., such as the Galaxy Tab from Samsung Electronics Co., Ltd. In an alternative embodiment, the programming computer is a personal digital assistant handheld computer operating under the Pocket-PC, Windows Mobile, Windows Phone, Windows RT, or Windows operating systems, licensed by Microsoft Corporation, Redmond, Wash., such as the Surface from Microsoft Corporation, the Dell Axim X5 and X50 personal data assistants, sold by Dell, Inc., Round Top, Tex., the HP Jornada personal data assistant, sold by Hewlett-Packard Company, Palo Alto, Tex. The programming computer 41 functions through those components conventionally found in such devices, including, for instance, a central processing unit, volatile and persistent memory, touch-sensitive display, control buttons, peripheral input and output ports, and network interface. The computer 41 operates under the control of the application software 45, which is executed as program code as a series of process or method modules or steps by the programmed computer hardware. Other assemblages or configurations of computer hardware, firmware, and software are possible.

Operationally, the programming computer 41, when connected to a neurostimulator 12 through wireless telemetry using the programming wand 42, can be used by a healthcare provider to remotely interrogate the neurostimulator 12 and modify stored stimulation parameters. The programming wand 42 provides data conversion between the digital data accepted by and output from the programming computer and the radio frequency signal format that is required for communication with the neurostimulator 12. The programming computer 41 may further be configured to receive inputs, such as physiological signals received from patient sensors (e.g., implanted or external). These sensors may be configured to monitor one or more physiological signals, e.g., vital signs, such as body temperature, pulse rate, respiration rate, blood pressure, etc. These sensors may be coupled directly to the programming computer 41 or may be coupled to another instrument or computing device which receives the sensor input and transmits the input to the programming computer 41. The programming computer 41 may monitor, record, and/or respond to the physiological signals in order to effectuate stimulation delivery in accordance with embodiments of the present invention.

The healthcare provider operates the programming computer 41 through a user interface that includes a set of input controls 43 and a visual display 44, which could be touch-sensitive, upon which to monitor progress, view downloaded telemetry and recorded physiology, and review and modify programmable stimulation parameters. The telemetry can include reports on device history that provide patient identifier, implant date, model number, serial number, magnet activations, total ON time, total operating time, manufacturing date, and device settings and stimulation statistics and on device diagnostics that include patient identifier, model identifier, serial number, firmware build number, implant date, communication status, output current status, measured current delivered, lead impedance, and battery status. Other kinds of telemetry or telemetry reports are possible.

During interrogation, the programming wand 42 is held by its handle 46 and the bottom surface 47 of the programming wand 42 is placed on the patient's chest over the location of the implanted neurostimulator 12. A set of indicator lights 49 can assist with proper positioning of the wand and a set of input controls 48 enable the programming wand 42 to be operated directly, rather than requiring the healthcare provider to awkwardly coordinate physical wand manipulation with control inputs via the programming computer 41. The sending of programming instructions and receipt of telemetry information occur wirelessly through radio frequency signal interfacing. Other programming computer and programming wand operations are possible.

FIG. 4 is a diagram showing the helical electrodes 14 provided as on the stimulation lead assembly 13 of FIG. 2 in place on a vagus nerve 15, 16 in situ 50. Although described with reference to a specific manner and orientation of implantation, the specific surgical approach and implantation site selection particulars may vary, depending upon physician discretion and patient physical structure.

Under one embodiment, helical electrodes 14 may be positioned on the patient's vagus nerve 61 oriented with the end of the helical electrodes 14 facing the patient's head. At the distal end, the insulated electrical lead body 13 is bifurcated into a pair of lead bodies 57, 58 that are connected to a pair of electrodes 51, 52. The polarity of the electrodes 51, 52 could be configured into a monopolar cathode, a proximal anode and a distal cathode, or a proximal cathode and a distal anode. In addition, an anchor tether 53 is fastened over the lead bodies 57, 58 that maintains the helical electrodes' position on the vagus nerve 61 following implant. In one embodiment, the conductors of the electrodes 51, 52 are manufactured using a platinum and iridium alloy, while the helical materials of the electrodes 51, 52 and the anchor tether 53 are a silicone elastomer.

During surgery, the electrodes 51, 52 and the anchor tether 53 are coiled around the vagus nerve 61 proximal to the patient's head, each with the assistance of a pair of sutures 54, 55, 56, made of polyester or other suitable material, which help the surgeon to spread apart the respective helices. The lead bodies 57, 58 of the electrodes 51, 52 are oriented distal to the patient's head and aligned parallel to each other and to the vagus nerve 61. A strain relief bend 60 can be formed on the distal end with the insulated electrical lead body 13 aligned, for example, parallel to the helical electrodes 14 and attached to the adjacent fascia by a plurality of tie-downs 59 a-b.

The neurostimulator 12 delivers VNS under control of the electronic circuitry 22. The stored stimulation parameters are programmable. Each stimulation parameter can be independently programmed to define the characteristics of the cycles of therapeutic stimulation and inhibition to ensure optimal stimulation for a patient 10. The programmable stimulation parameters include output current, signal frequency, pulse width, signal ON time, signal OFF time, magnet activation (for VNS specifically triggered by “magnet mode”), and reset parameters. Other programmable parameters are possible. In addition, sets or “profiles” of preselected stimulation parameters can be provided to physicians with the external programmer and fine-tuned to a patient's physiological requirements prior to being programmed into the neurostimulator 12, such as described in commonly-assigned U.S. patent application entitled “Computer-Implemented System and Method for Selecting Therapy Profiles of Electrical Stimulation of Cervical Vagus Nerves for Treatment of Chronic Cardiac Dysfunction,” Ser. No. 13/314,138, filed on Dec. 7, 2011, published as U.S. Patent Publication no. 2013-0158618 A1, pending, the disclosure of which is incorporated by reference.

Therapeutically, the VNS may be delivered as a multimodal set of therapeutic doses, which are system output behaviors that are pre-specified within the neurostimulator 12 through the stored stimulation parameters and timing cycles implemented in firmware and executed by the microprocessor controller. The therapeutic doses include a maintenance dose that includes continuously-cycling, intermittent and periodic cycles of electrical stimulation during periods in which the pulse amplitude is greater than 0 mA (“therapy ON”) and during periods in which the pulse amplitude is 0 mA (“therapy OFF”).

The neurostimulator 12 can operate either with or without an integrated heart rate sensor, such as respectively described in commonly-assigned U.S. Pat. No. 8,577,458, entitled “Implantable Device for Providing Electrical Stimulation of Cervical Vagus Nerves for Treatment of Chronic Cardiac Dysfunction with Leadless Heart Rate Monitoring,” and U.S. patent application, entitled “Implantable Device for Providing Electrical Stimulation of Cervical Vagus Nerves for Treatment of Chronic Cardiac Dysfunction,” Ser. No. 13/314,119, filed on Dec. 7, 2011, pending, the disclosures of which are hereby incorporated by reference herein in their entirety. Additionally, where an integrated leadless heart rate monitor is available, the neurostimulator 12 can provide autonomic cardiovascular drive evaluation and self-controlled titration, such as respectively described in commonly-assigned U.S. patent application entitled “Implantable Device for Evaluating Autonomic Cardiovascular Drive in a Patient Suffering from Chronic Cardiac Dysfunction,” Ser. No. 13/314,133, filed on Dec. 7, 2011, U.S. Patent Publication No. 2013-0158616 A1, pending, and U.S. patent application entitled “Implantable Device for Providing Electrical Stimulation of Cervical Vagus Nerves for Treatment of Chronic Cardiac Dysfunction with Bounded Titration,” Ser. No. 13/314,135, filed on Dec. 7, 2011, U.S. Patent Publication No. 2013-0158617 A1, pending, the disclosures of which are incorporated by reference. Finally, the neurostimulator 12 can be used to counter natural circadian sympathetic surge upon awakening and manage the risk of cardiac arrhythmias during or attendant to sleep, particularly sleep apneic episodes, such as respectively described in commonly-assigned U.S. patent application entitled “Implantable Neurostimulator-Implemented Method For Enhancing Heart Failure Patient Awakening Through Vagus Nerve Stimulation,” Ser. No. 13/673,811, filed on Nov. 9, 2012, pending, the disclosure of which is incorporated by reference.

The VNS stimulation signal may be delivered as a therapy in a maintenance dose having an intensity that is insufficient to elicit undesirable side effects, such as cardiac arrhythmias. The VNS can be delivered with a periodic duty cycle in the range of 2% to 89% with a preferred range of around 4% to 36% that is delivered as a low intensity maintenance dose. Alternatively, the low intensity maintenance dose may comprise a narrow range approximately at 17.5%, such as around 15% to 25%. The selection of duty cycle is a tradeoff among competing medical considerations. The duty cycle is determined by dividing the stimulation ON time by the sum of the ON and OFF times of the neurostimulator 12 during a single ON-OFF cycle. However, the stimulation time may also need to include ramp-up time and ramp-down time, where the stimulation frequency exceeds a minimum threshold (as further described infra with reference to FIG. 7).

FIG. 5 is a graph 70 showing, by way of example, the relationship between the targeted therapeutic efficacy 73 and the extent of potential side effects 74 resulting from use of the implantable neurostimulator 12 of FIG. 1, after the patient has completed the titration process. The graph in FIG. 5 provides an illustration of the failure of increased stimulation intensity to provide additional therapeutic benefit, once the stimulation parameters have reached the neural fulcrum zone, as will be described in greater detail below with respect to FIG. 8. As shown in FIG. 5, the x-axis represents the duty cycle 71. The duty cycle is determined by dividing the stimulation ON time by the sum of the ON and OFF times of the neurostimulator 12 during a single ON-OFF cycle. However, the stimulation time may also include ramp-up time and ramp-down time, where the stimulation frequency exceeds a minimum threshold (as further described infra with reference to FIG. 7). When including the ramp-up and ramp-down times, the total duty cycle may be calculated as the ON time plus the ramp-up and ramp-down times divided by the OFF time, ON time, and ramp-up and ramp-down times, and may be, e.g., between 15% and 30%, and more specifically approximately 23%. The y-axis represents physiological response 72 to VNS therapy. The physiological response 72 can be expressed quantitatively for a given duty cycle 71 as a function of the targeted therapeutic efficacy 73 and the extent of potential side effects 74, as described infra. The maximum level of physiological response 72 (“max”) signifies the highest point of targeted therapeutic efficacy 73 or potential side effects 74.

Targeted therapeutic efficacy 73 and the extent of potential side effects 74 can be expressed as functions of duty cycle 71 and physiological response 72. The targeted therapeutic efficacy 73 represents the intended effectiveness of VNS in provoking a beneficial physiological response for a given duty cycle and can be quantified by assigning values to the various acute and chronic factors that contribute to the physiological response 72 of the patient 10 due to the delivery of therapeutic VNS. Acute factors that contribute to the targeted therapeutic efficacy 73 include beneficial changes in heart rate variability and increased coronary flow, reduction in cardiac workload through vasodilation, and improvement in left ventricular relaxation. Chronic factors that contribute to the targeted therapeutic efficacy 73 include improved cardiovascular regulatory function, as well as decreased negative cytokine production, increased baroreflex sensitivity, increased respiratory gas exchange efficiency, favorable gene expression, renin-angiotensin-aldosterone system down-regulation, anti-arrhythmic, anti-apoptotic, and ectopy-reducing anti-inflammatory effects. These contributing factors can be combined in any manner to express the relative level of targeted therapeutic efficacy 73, including weighting particular effects more heavily than others or applying statistical or numeric functions based directly on or derived from observed physiological changes. Empirically, targeted therapeutic efficacy 73 steeply increases beginning at around a 5% duty cycle, and levels off in a plateau near the maximum level of physiological response at around a 30% duty cycle. Thereafter, targeted therapeutic efficacy 73 begins decreasing at around a 50% duty cycle and continues in a plateau near a 25% physiological response through the maximum 100% duty cycle.

The intersection 75 of the targeted therapeutic efficacy 73 and the extent of potential side effects 74 represents one optimal duty cycle range for VNS. FIG. 6 is a graph 80 showing, by way of example, the optimal duty cycle range 83 based on the intersection 75 depicted in FIG. 5. The x-axis represents the duty cycle 81 as a percentage of stimulation time over stimulation time plus inhibition time. The y-axis represents therapeutic points 82 reached in operating the neurostimulator 12 at a given duty cycle 81. The optimal duty range 83 is a function 84 of the intersection 75 of the targeted therapeutic efficacy 73 and the extent of potential side effects 74. The therapeutic operating points 82 can be expressed quantitatively for a given duty cycle 81 as a function of the values of the targeted therapeutic efficacy 73 and the extent of potential side effects 74 at their point of intersection in the graph 70 of FIG. 5. The optimal therapeutic operating point 85 (“max”) signifies a tradeoff that occurs at the point of highest targeted therapeutic efficacy 73 in light of lowest potential side effects 74 and that point will typically be found within the range of a 5% to 30% duty cycle 81. Other expressions of duty cycles and related factors are possible.

Therapeutically and in the absence of patient physiology of possible medical concern, such as cardiac arrhythmias, VNS is delivered in a low level maintenance dose that uses alternating cycles of stimuli application (ON) and stimuli inhibition (OFF) that are tuned to activate both afferent and efferent pathways. Stimulation results in parasympathetic activation and sympathetic inhibition, both through centrally-mediated pathways and through efferent activation of preganglionic neurons and local circuit neurons. FIG. 7 is a timing diagram showing, by way of example, a stimulation cycle and an inhibition cycle of VNS 90, as provided by implantable neurostimulator 12 of FIG. 1. The stimulation parameters enable the electrical stimulation pulse output by the neurostimulator 12 to be varied by both amplitude (output current 96) and duration (pulse width 94). The number of output pulses delivered per second determines the signal frequency 93. In one embodiment, a pulse width in the range of 100 to 250 μSec delivers between 0.02 mA and 50 mA of output current at a signal frequency of about 10 Hz, although other therapeutic values could be used as appropriate. In general, the stimulation signal delivered to the patient may be defined by a stimulation parameter set comprising at least an amplitude, a frequency, a pulse width, and a duty cycle.

In one embodiment, the stimulation time is considered the time period during which the neurostimulator 12 is ON and delivering pulses of stimulation, and the OFF time is considered the time period occurring in-between stimulation times during which the neurostimulator 12 is OFF and inhibited from delivering stimulation.

In another embodiment, as shown in FIG. 7, the neurostimulator 12 implements a stimulation time 91 comprising an ON time 92, a ramp-up time 97 and a ramp-down time 98 that respectively precede and follow the ON time 92. Under this embodiment, the ON time 92 is considered to be a time during which the neurostimulator 12 is ON and delivering pulses of stimulation at the full output current 96. Under this embodiment, the OFF time 95 is considered to comprise the ramp-up time 97 and ramp-down time 98, which are used when the stimulation frequency is at least 10 Hz, although other minimum thresholds could be used, and both ramp-up and ramp-down times 97, 98 last two seconds, although other time periods could also be used. The ramp-up time 97 and ramp-down time 98 allow the strength of the output current 96 of each output pulse to be gradually increased and decreased, thereby avoiding deleterious reflex behavior due to sudden delivery or inhibition of stimulation at a programmed intensity.

Therapeutic vagus neural stimulation has been shown to provide cardioprotective effects. Although delivered in a maintenance dose having an intensity that is insufficient to elicit undesirable side effects, such as cardiac arrhythmias, ataxia, coughing, hoarseness, throat irritation, voice alteration, or dyspnea, therapeutic VNS can nevertheless potentially ameliorate pathological tachyarrhythmias in some patients. Although VNS has been shown to decrease defibrillation threshold, VNS has not been shown to terminate VF in the absence of defibrillation. VNS prolongs ventricular action potential duration, so may be effective in terminating VT. In addition, the effect of VNS on the AV node may be beneficial in patients with AF by slowing conduction to the ventricles and controlling ventricular rate.

Neural Fulcrum Zone

As described above, autonomic regulation therapy results in simultaneous creation of action potentials that simultaneously propagate away from the stimulation site in afferent and efferent directions within axons comprising the cervical vagus nerve complex. Upon stimulation of the cervical vagus nerve, action potentials propagate away from the stimulation site in two directions, efferently toward the heart and afferently toward the brain. Different parameter settings for the neurostimulator 12 may be adjusted to deliver varying stimulation intensities to the patient. The various stimulation parameter settings for current VNS devices include output current amplitude, signal frequency, pulse width, signal ON time, and signal OFF time.

When delivering neurostimulation therapies to patients, it is generally desirable to avoid stimulation intensities that result in either excessive tachycardia or excessive bradycardia. However, researchers have typically utilized the patient's heart rate changes as a functional response indicator or surrogate for effective recruitment of nerve fibers and engagement of the autonomic nervous system elements responsible for regulation of heart rate, which may be indicative of therapeutic levels of VNS. Some researchers have proposed that heart rate reduction caused by VNS stimulation is itself beneficial to the patient.

In accordance with some embodiments, a neural fulcrum zone is identified, and neurostimulation therapy is delivered within the neural fulcrum zone. This neural fulcrum zone corresponds to a combination of stimulation parameters at which autonomic engagement is achieved but for which a functional response determined by heart rate change is nullified due to the competing effects of afferently and efferently-transmitted action potentials. In this way, the tachycardia-inducing stimulation effects are offset by the bradycardia-inducing effects, thereby minimizing side effects such as significant heart rate changes while providing a therapeutic level of stimulation. One method of identifying the neural fulcrum zone is by delivering a plurality of stimulation signals at a fixed frequency but with one or more other parameter settings changed so as to gradually increase the intensity of the stimulation.

FIGS. 8A-8C provide illustrative charts reflecting the location of the neural fulcrum zone. FIG. 8A is a chart 800 illustrating a heart rate response in response to such a gradually increased intensity at a first frequency, in accordance with embodiments of the present invention. In this chart 800, the x-axis represents the intensity level of the stimulation signal, and the y-axis represents the observed heart rate change from the patient's baseline basal heart rate observed when no stimulation is delivered. In this example, the stimulation intensity is increased by increasing the output current amplitude.

A first set 810 of stimulation signals is delivered at a first frequency (e.g., 10 Hz). Initially, as the intensity (e.g., output current amplitude) is increased, a tachycardia zone 851-1 is observed, during which period, the patient experiences a mild tachycardia. As the intensity continues to be increased for subsequent stimulation signals, the patient's heart rate response begins to decrease and eventually enters a bradycardia zone 853-1, in which a bradycardia response is observed in response to the stimulation signals. As described above, the neural fulcrum zone is a range of stimulation parameters at which the functional effects from afferent activation are balanced with or nullified by the functional effects from efferent activation to avoid extreme heart rate changes while providing therapeutic levels of stimulation. In accordance with some embodiments, the neural fulcrum zone 852-1 can be located by identifying the zone in which the patient's response to stimulation produces either no heart rate change or a mildly decreased heart rate change (e.g., <5% decrease, or a target number of beats per minute). As the intensity of stimulation is further increased at the fixed first frequency, the patient enters an undesirable bradycardia zone 853-1. In these embodiments, the patient's heart rate response is used as an indicator of autonomic engagement. In other embodiments, other physiological responses may be used to indicate the zone of autonomic engagement at which the propagation of efferent and afferent action potentials are balanced, the neural fulcrum zone.

FIG. 8B is a chart 860 illustrating a heart rate response in response to such a gradually increased intensity at two additional frequencies, in accordance with embodiments of the present invention. In this chart 860, the x-axis and y-axis represent the intensity level of the stimulation signal and the observed heart rate change, respectively, as in FIG. 8A, and the first set 810 of stimulation signals from FIG. 8A is also shown.

A second set 810 of stimulation signals is delivered at a second frequency lower than the first frequency (e.g., 5 Hz). Initially, as the intensity (e.g., output current amplitude) is increased, a tachycardia zone 851-2 is observed, during which period, the patient experiences a mild tachycardia. As the intensity continues to be increased for subsequent stimulation signals, the patient's heart rate response begins to decrease and eventually enters a bradycardia zone 853-2, in which a bradycardia response is observed in response to the stimulation signals. The low frequency of the stimulation signal in the second set 820 of stimulation signals limits the functional effects of nerve fiber recruitment and, as a result, the heart response remains relatively limited. Although this low frequency stimulation results in minimal side effects, the stimulation intensity is too low to result in effective recruitment of nerve fibers and engagement of the autonomic nervous system. As a result, a therapeutic level of stimulation is not delivered.

A third set of 830 of stimulation signals is delivered at a third frequency higher than the first and second frequencies (e.g., 20 Hz). As with the first set 810 and second set 820, at lower intensities, the patient first experiences a tachycardia zone 851-3. At this higher frequency, the level of increased heart rate is undesirable. As the intensity is further increased, the heart rate decreases, similar to the decrease at the first and second frequencies but at a much higher rate. The patient first enters the neural fulcrum zone 852-3 and then the undesirable bradycardia zone 853-3. Because the slope of the curve for the third set 830 is much steeper than the second set 820, the region in which the patient's heart rate response is between 0% and −5% (e.g., the neural fulcrum zone 852-3) is much narrower than the neural fulcrum zone 852-2 for the second set 820. Accordingly, when testing different operational parameter settings for a patient by increasing the output current amplitude by incremental steps, it can be more difficult to locate a programmable output current amplitude that falls within the neural fulcrum zone 852-3. When the slope of the heart rate response curve is high, the resulting heart rate may overshoot the neural fulcrum zone and create a situation in which the functional response transitions from the tachycardia zone 851-3 to the undesirable bradycardia zone 853-3 in a single step. At that point, the clinician would need to reduce the amplitude by a smaller increment or reduce the stimulation frequency in order to produce the desired heart rate response for the neural fulcrum zone 852-3.

FIG. 8C is a chart 880 illustrating mean heart rate response surfaces in conscious, normal dogs during 14 second periods of right cervical vagus VNS stimulation ON-time. The heart rate responses shown in z-axis represent the percentage heart rate change from the baseline heart rate at various sets of VNS parameters, with the pulse width the pulse width set at 250 μsec, the pulse amplitude ranging from 0 mA to 3.5 mA (provided by the x-axis) and the pulse frequency ranging from 2 Hz to 20 Hz (provided by the y-axis). Curve 890 roughly represents the range of stimulation amplitude and frequency parameters at which a null response (i.e., 0% heart rate change from baseline) is produced. This null response curve 890 is characterized by the opposition of functional responses (e.g., tachycardia and bradycardia) arising from afferent and efferent activation.

Closed-Loop Neurostimulation

As described above, embodiments of the implanted device may include a physiological sensor, such as a heart rate sensor or a blood pressure sensor, configured to monitor a physiological signal from the patient over extended periods of time on an ambulatory basis. In accordance with embodiments of the present invention, the implanted device may be configured to adjust stimulation parameters to maintain stimulation in the neural fulcrum zone based on detected changes in the physiological response to stimulation.

In some embodiments described above, the identification of the neural fulcrum zone and the programming of the stimulation parameters to deliver stimulation signals in the neural fulcrum zone may be performed in a clinic by a health care provider. In some embodiments, the implanted medical device may be configured to automatically monitor the patient's physiological response using an implanted physiological sensor to initially identify the neural fulcrum zone and set the stimulation parameters to deliver signals in the neural fulcrum zone. In addition, under certain circumstances, the patient's physiological response to those initial stimulation parameters may change. This change could occur as the stimulation is chronically delivered over an extended period of time as the patient's body adjusts to the stimulation. Alternatively, this change could occur as a result of other changes in the patient's condition, such as changes in the patient's medication, disease state, circadian rhythms, or other physiological change.

If the changes in the patient's response to stimulation results in a change in the patient's response curve, the initially identified stimulation parameters may no longer deliver stimulation in the neural fulcrum zone. Therefore, it may be desirable for the implanted medical device to automatically adjust one or more stimulation parameters (e.g., pulse amplitude) so that subsequent stimulation signals may be delivered in the neural fulcrum zone. For example, in embodiments described above, where the monitored physiological response is the patient's heart rate, then if tachycardia is later detected in response to stimulation signals that had previously resulted in a transition heart rate response, the IMD may be configured to automatically increase the pulse amplitude (or other stimulation parameters) until a transition heart rate response is again detected. Subsequent stimulation may continue to be delivered using the new stimulation parameters until another change in the patient's physiological response is detected.

In some embodiments, the patient's physiological response may be substantially continuously monitored. In other embodiments, the patient's physiological response may be monitored on a periodic basis, such as, for example, every minute, hour, day, or other periodic or aperiodic schedule that may be desired in order to provide the desired monitoring schedule. In other embodiments, the patient's physiological response may be monitored in response to a control signal delivered by an external device, such as a control magnet or wireless data signal from a programming wand. The external control signal to initiate monitoring may be delivered when it is desired to monitor the physiological response when a patient condition is changing, such as when the patient is about to take a medication, is about to go to sleep, or has just awoken from sleep. In some embodiments, the external control signal may be used by the patient when an automatically increasing stimulation intensity in response to monitoring physiological signals is causing undesirable side effects. When the IMD receives such a control signal, the IMD may be programmed to automatically reduce the stimulation intensity until the side effects are alleviated (as indicated, for example, by a subsequent control input).

Implantable VNS and Carotid Baroreceptor Stimulation System

Patients suffering from chronic heart failure frequently also suffer from hypertension. Hypertension causes a distortion of the arterial wall, which stimulates stretch-sensitive baroreceptors contained in the carotid artery. The application of an electrical field to the carotid sinus wall to electrically stimulate the carotid baroreceptor has been proposed as a therapy for blood pressure reduction. In accordance with embodiments of the present invention, combination stimulation systems are provided which deliver VNS stimulation for treating CHF, as described in greater detail above, along with carotid baroreceptor stimulation (CBS) for treating hypertension, as will be described in greater detail below. Combining the VNS functionality with the CBS functionality into a single implantable device provides an integrated therapy system for two common comorbidities, and can minimize implant size, invasiveness, and complexity of implantation surgery, as well as provide other therapeutic advantages described below.

FIGS. 9A-9G are front anatomical diagrams showing, by way of example, various implantable VNS/CBS systems in accordance with embodiments of the present invention. FIG. 9A provides a simplified illustration of certain anatomic features of a human subject 10 pertinent to the VNS/CBS stimulation systems. The left ventricle of the subject's heart pumps oxygenated blood into the aortic arch 901. The left common carotid artery 902L and the right common carotid artery 902R extend from the aortic arch 901 towards the brain. The left common carotid artery 902L bifurcates into the left internal carotid artery 906L and the left external carotid artery 907L at the left carotid sinus 908L, and the right common carotid artery 902R bifurcates into the right internal carotid artery 906R and the right external carotid artery 907R at the right carotid sinus 908R. The left carotid sinus nerve 905L terminates at the left carotid baroreceptors and the right carotid sinus nerve 905R terminates at the right carotid baroreceptors 909R. The carotid baroreceptors are sensory nerve endings in the wall of the carotid sinus, which are sensitive to stretching of the wall resulting from increased pressure from within. The carotid baroreceptors are connected to the brain via the nervous system and function as the receptor of central reflex mechanisms that tend to reduce that pressure. The left vagus nerve 910L runs through the patient's neck roughly parallel to the common carotid artery 902L and in close proximity to the left carotid baroreceptor, and the right vagus nerve 91 OR runs roughly parallel to the common carotid artery 902R and in close proximity to the right carotid baroreceptor 909R.

FIG. 9A shows a single-lead VNS/CBS system 900 a, in accordance with embodiments of the present invention. The system 900 a comprises a pulse generation module 920 a having a CBS electrode assembly 940 a for providing CBS stimulation, and a VNS electrode assembly 950 a for providing VNS stimulation, as described above with respect to FIG. 1. In the embodiment illustrated in FIG. 9A, the CBS electrode assembly 940 a and VNS electrode assembly 950 a are provided as part of a single lead assembly 930 a, which has single connector coupled to a header on the pulse generation module 920 a. In other embodiments, such as those described below, other configurations may be used.

The CBS electrode assembly 940 a may comprise any type of electrode suitable for delivering electrical stimulation to activate the carotid baroreceptors to induce the baroreflex system. A variety of electrode configurations have been used by others to stimulate the baroreceptors and may be suitable for use various embodiments. For example, the CBS electrode assembly 940 a may comprise a coil or patch electrode positioned over the exterior of the carotid sinus 908L near the carotid bifurcation. The VNS electrode assembly 950 a may comprise any type of electrode suitable for delivering electrical stimulation to the vagus nerve 910L, such as, e.g., a bipolar electrode described above with respect to FIG. 1A. The first lead assembly 930 a may comprise a silicone or polyurethane insulation surrounding conductive leads which conduct electrical current between the pulse generation module 920 a and the electrode assemblies. Any of a variety of electrode assemblies may be used in accordance with embodiments of the present invention.

Sensing electrodes (not shown) may also be provided at an intermediate position along the lead assembly 930 a or as part of a separate lead assembly for detecting subcutaneous electrocardiographic (ECG) signals. This detected ECG can be used to determine the patient's heart rate, including changes to the heart rate in response to either VNS or CBS stimulation or to other changes in the patient's physical state. In other embodiments, one or more of the stimulation electrode assemblies (e.g., the CBS electrode assembly 940 a or the VNS electrode assembly 950 a) and/or the housing of the pulse generation module 920 a may be used for sensing ECG in addition to the sensing electrodes to provide additional ECG sensing vectors, or in place of the dedicated sensing electrodes to reduce the total number of electrodes in the system 900 a. In some embodiments, a transvascular pressure sensor may be used measure deflections in a vascular wall in order to determine arterial blood pressure. In some embodiments, this transvascular pressure sensor may be integrated into the CBS electrode assembly, such that both the pressure sensing components and the CBS electrode contacts may be integrated into a single cuff structure that is positioned around the carotid sinus.

FIG. 10 is a simplified block diagram of the implantable pulse generation module 920 a. The pulse generation module 920 a comprises a CBS subsystem 1010, a VNS subsystem 1020, a header assembly 1040, a control system 1030, a memory 1032, a communications interface 1034, a battery 1036, and an ECG sensing module 1016. The control system 1102 comprises a processor and other logic programmed to control the operation of the pulse generation module 920 a. The memory 1032 may be used to store operational parameters for the pulse generation module 920 a and data regarding sensed physiological signals and stimulation delivery. The communications interface 1034 may be used to communicate with other devices, such as an external programmer for programming and retrieving data from the module 920 a, or one or more implanted or external sensors for detecting ECG or other patient physiological signals. The communications interface 1034 may comprise any of a variety of wireless communication systems suitable for use with an implanted device. The battery 1036 may comprise any type of battery suitable for powering the module 920 a, such as a lithium carbon monofluoride primary battery or a rechargeable secondary cell battery. Because the power demands of CBS and VNS differ, in some embodiments, separate batteries may be used for powering the CBS subsystem 1010 and the VNS subsystem 1020.

The CBS subsystem 1010 comprises a CBS pulse generator 1012 and the VNS subsystem 1020 comprises a VNS pulse generator 1022. The CBS pulse generator 1012 and the VNS pulse generator 1022 are conceptually illustrated in FIG. 10 as separate blocks, but may be implemented as separate hardware components (e.g., separate logic and electronic components), or may be implemented using common hardware components.

In various embodiments, the pulse generation module 920 a may be implanted in a variety of locations within the patient's body. For example, the module 920 a may be positioned subcutaneously on either the left side, right side, or medial position in the patient's chest between the skin and the rib cage, proximal to, distal from, or overlapping the sternum, in an axillary location, or in a posterior location. The embodiment illustrated in FIG. 9A utilizes a single lead assembly 930 a so that only a single lead is tunneled through the patient's neck to the pulse generation module 920 a. This can reduce the challenges associated with tunneling multiple leads through the patient's neck. Because of the close proximity of the vagus nerve 910L to the left carotid baroreceptors, the two neural targets for stimulation are located in the same general region in the patient's neck. Accordingly, the implantation of the CBS electrode assembly 940 a for providing CBS stimulation and the VNS electrode assembly 950 a for providing VNS stimulation may be performed via a single incision in the patient's neck, thereby minimizing the invasiveness of the implantation surgery. In some embodiments, the surgical techniques used for coupling the CBS electrode assembly 940 a for providing CBS stimulation and the VNS electrode assembly 950 a for providing VNS stimulation may be very similar, thereby minimizing the amount of additional surgical training required for the implanting physician.

Any techniques for carotid baroreceptor stimulation may be utilized in the operation of the CBS function of VNS/CBS system, in accordance with embodiments of the present invention. The CBS stimulation intensity may be configured to deliver stimulation at any desired therapeutic level. The output signal may be, for example, constant current or constant voltage. In embodiments using a modulated signal, wherein the output signal comprises, for example, a series of pulses, any of the stimulation pulse parameters may be adjusted, including, for example, amplitude, frequency, pulse width, pulse waveform, pulse polarity, and pulse phase (e.g., monophasic or biphasic). For example, the CBS subsystem 1010 may deliver a rectangular pulse stimulation signal at a fixed intensity, e.g., with a stimulation amplitude ranging from approximately 0.5 mA to approximately 7.0 mA, a stimulation frequency between approximately 20 Hz and approximately 100 Hz, and a pulse width of approximately 500 μsec.

In some embodiments, the output signal for CBS stimulation may have a fixed waveform and intensity delivered intermittently at a high duty cycle 24 hours a day. In accordance with other embodiments of the present invention, the VNS and CBS stimulation therapies may be adjusted based on time of day, patient status, or other variable, and the VNS and CBS stimulation may be delivered in a coordinated fashion.

Humans typically have a greater metabolic demand during waking hours than during periods of sleep. Due to variation in a subject's activity levels over the course of the day, heart rate regulation is more complicated than during periods of sleep, when the subject's metabolic fluctuations decrease. In addition, during periods of sleep, the subject's average heart rate and blood pressure are generally lower than during waking hours. Accordingly, in some embodiments, it may be desirable to modify either or both the CBS and VNS stimulation parameters to optimize for the variable demands of sleep and wake time. In some embodiments, the pulse generation module 920 a may include an internal clock, so the periods of sleep and wake may be estimated based on the time of day, such that a certain window of time during the night (e.g., between 1 am-6 am or other time period during which the subject 10 typically sleeps) are assumed to be periods of sleep and the remaining times are assumed to be periods of awake time. In other embodiments, sensors may be used in place of or in addition to the internal clock to estimate sleep/wake times. For example, the control system 1030 may assume the subject is sleeping based on the heart rate changes detected by the ECG sensing module 1016. A reduced heart rate over an extended period of time or during evening hours may indicate that the subject is asleep. The pulse generation module 920 a may also utilize movement sensors, such as accelerometers and inclinometers, to estimate the subject's sleep/wake state. For example, an absence of movement in the subject or a prolonged period of a reclined position may be indicative of sleep, particularly when observed during periods of reduced heart rate.

In accordance with embodiments of the present invention, different stimulation parameters may be used depending on the subject's estimated sleep/wake state. In some embodiments, the intensity of the CBS and/or VNS stimulation may be reduced at night due to the decreased metabolic demands. In other embodiments, the intensity of the CBS and/or VNS stimulation may be increased at night due to a potential increase in the subject's tolerance for side effects resulting from the increased stimulation intensity during sleep.

In other embodiments, different stimulation parameters may be used depending on changes in the patient's physiological state. It may be desirable to increase or decrease one or both of the CBS and VNS stimulation parameters in response to detected state changes. If both the CBS and VNS therapies are being modified, the increases or decreases in the stimulation parameters may occur simultaneously or alternately. In some embodiments, different stimulation parameters may be used depending on the patient's activity level, which may be estimated based on the patient's heart rate and/or movement. In this case, the CBS therapy may be temporarily suspended during periods of increased activity levels, which would be indicative of exercise or other vigorous activity.

The control system may be configured to coordinate the delivery of the CBS and VNS therapies. In some embodiments, it may be desirable for the CBS and VNS therapies to be delivered with the same stimulation parameter settings. In other embodiments, it may be desirable for the therapies to be delivered with different parameter settings. For example, the control system may configured to activate the VNS subsystem to deliver electrical stimulation with a first stimulation parameter and to activate the CBS subsystem to deliver electrical stimulation with a second stimulation parameter different than the first stimulation parameter. The first and second stimulation parameters may correspond to one or more of the following parameters: stimulation amplitude, stimulation frequency, stimulation pulse width, or stimulation duty cycle.

As described above, any variety of system configurations may be used in various embodiments. FIG. 9B is front anatomical diagram showing a single-lead VNS/CBS system 900 b, in accordance with other embodiments of the present invention. The system 900 b comprises a pulse generation module 910 b having a single lead assembly 920 b, similar to lead assembly 920 a in FIG. 9A, except that the CBS electrode assembly 940 b is provided at a distal end of the lead assembly 920 b, and the VNS electrode assembly 950 b is provided at an intermediate point between the CBS electrode assembly 940 b and the pulse generation module 920 b. This arrangement may be preferable over the arrangement illustrated in FIG. 9A, depending on the desired routing of the lead assembly 920 a to reach the two neural stimulation targets.

FIG. 9C is front anatomical diagram showing a single bifurcated lead VNS/CBS system 900 c, in accordance with other embodiments of the present invention. The system 900 c comprises a bifurcated lead assembly 930 c, which comprises a bifurcated portion 932 c leading to a CBS lead portion 934 c and a VNS lead portion 935 c. The CBS electrode assembly 940 c is provided at a distal end of the CBS lead portion 934 c and VNS electrode assembly 950 c is provided at a distal end of the VNS lead portion 935 c. This configuration may advantageously provide a single lead body to tunnel between the pulse generation module 920 c and the subject's neck, while also providing increased flexibility in positioning the CBS electrode assembly 940 c and VNS electrode assembly 950 c at the desired location in the subject.

FIG. 9D is front anatomical diagram showing a two lead VNS/CBS system 920 d, in accordance with other embodiments of the present invention. The system 920 d comprises a pulse generation module 910 d coupled to the proximal connector of a CBS lead assembly 936 d and the proximal connector of a separate VNS lead assembly 937 d. The CBS electrode assembly 940 d is provided at a distal end of the CBS lead assembly 936 d and VNS electrode assembly 950 d is provided at a distal end of the VNS lead assembly 937 d. This configuration may advantageously provide increased flexibility in positioning the CBS electrode assembly 940 d and VNS electrode assembly 950 d at the desired location in the subject. Although FIG. 9D shows both the CBS electrode assembly 940 d and VNS electrode assembly 950 d positioned on the left side of the subject's neck, in other embodiments, a first one of the electrode assemblies may be positioned on an opposite side of the subject's neck from a second one of the electrode assemblies.

FIG. 9E is front anatomical diagram showing a two lead, bilateral VNS/CBS system 900 e, in accordance with other embodiments of the present invention. The system 900 e comprises a pulse generation module 920 e coupled to a proximal connector of a CBS lead assembly 936 e and a proximal connector of a VNS lead assembly 937 e. In the illustrated embodiment, the CBS lead assembly 936 e comprises a bifurcated portion 932 e leading to a first CBS lead portion 934 e-1 and a second CBS lead portion 934 e-2. A first CBS electrode assembly 940 e-1 at the distal end of the first CBS lead portion 934 e-1 is positioned to stimulate the subject's left baroreceptors, and a second CBS electrode assembly 940 e-2 at the distal end of the second CBS lead portion 934 e-2 is positioned to stimulate the subject's right baroreceptors. This embodiment enables the bilateral stimulation of the carotid baroreceptors, along with the stimulation of the left vagus nerve.

FIG. 9F is front anatomical diagram showing a two lead, bilateral VNS/CBS system 900 f, in accordance with other embodiments of the present invention. The system 900 f comprises a pulse generation module 920 f coupled to a proximal connector of a first bifurcated lead assembly 936 f-1 and a proximal connector of a second bifurcated lead assembly 936 f-2. In the illustrated embodiment, the first lead assembly 936 f-1 comprises a bifurcated portion 932 f-1 leading to a first VNS lead portion 935 f-1 and a first CBS lead portion 935 f-2, which have a first VNS electrode assembly 950 f-1 and a first CBS electrode assembly 940 f-1 provided at distal ends thereof, respectively. A second lead assembly 936 f-2 similar to the first lead assembly 936 f-1, and comprises a bifurcated portion 932 f-2 leading to a second VNS lead portion 934 f-2 and a second CBS lead portion 934 f-2, which have a second VNS electrode assembly 950 f-2 and a second CBS electrode assembly 940 f-2 provided at distal ends thereof, respectively. This configuration enables bilateral CBS stimulation and bilateral VNS stimulation.

FIG. 9G is front anatomical diagram showing a single lead, single cuff VNS/CBS system 900 g, in accordance with other embodiments of the present invention. The system 900 g includes a cuff portion 950 g configured to wrap around both the carotid artery 906L and the vagus nerve 910L. The electrode contacts for both the CBS electrode assembly and the VNS electrode assembly are provided on an interior surface of the single cuff portion 950 g. Because of the close proximity of the carotid artery 906L to the vagus nerve 910L, it may be desirable to utilize a single component for coupling to both the carotid artery 906L to the vagus nerve 910L in order to reduce the number of implanted components and/or simplify implantation. In some embodiments, the cuff portion 950 g, which comprises a single structure that wraps around both the carotid artery 906L and the vagus nerve 910L, may include a cylindrical CBS sub-cuff that wraps around only the carotid artery 906L and includes the electrode contacts for the CBS electrode assembly and a cylindrical VNS sub-cuff that wraps around only the vagus nerve 910L and includes the electrode contacts for the VNS electrode assembly.

It will be understood that the configurations described in the various embodiments described above may vary to replace single lead assemblies with single bifurcated lead assemblies or two lead assemblies. For example, in FIG. 9F, the two bifurcated lead assemblies 936 f-1 and 936 f-2 may be replaced with single lead assemblies, similar to lead assembly 930 a in FIG. 9A or lead assembly 930 b in FIG. 9B.

In some embodiments described above, the pulse generation module, CBS electrode assemblies, and VNS electrode assemblies may be positioned on the same side of the patient's body. In other embodiments, one or more of these components of the VNS/CBS system may be positioned on different sides of the body. In particular, in some patients, it may be desirable for the VNS stimulation to be applied to the right vagus nerve, while providing CBS stimulation to the left baroreceptor.

In some embodiments, physiological sensors (e.g., ECG electrodes) may be positioned on one or more of the lead assemblies, the pulse generation module, or other structure, such as a separate sensor having a wired or wireless connection with the pulse generation module. In some embodiments, a respiration sensor may be provided along the lead assembly near the VNS electrode or the CBS electrode for sensing respiratory activity in the throat.

In some embodiments, the VNS functionality and the CBS functionality may operate independently, such that VNS stimulation is provided in accordance with any desired VNS therapeutic modality, and the CBS functionality is provided in accordance with any desired CBS therapeutic modality, without any coordination between the two therapies. In other embodiments, the control system 1030 of the VNS/CBS system may coordinate the VNS and CBS stimulation to provide improved therapeutic effect, as described above.

It will be understood that the VNS/baroreceptor stimulation systems described above are merely exemplary, and in other embodiments, different configurations may be used.

In various embodiments described above, the patient's heart rate response is used as the patient parameter indicative of the desired physiological response to VNS, and ECG is used to determine when changes to the CBS therapy are to occur. In other embodiments, different patient parameters may be monitored in conjunction with stimulation, including, for example, other heart rate variability parameters, ECG parameters such as PR interval and QT interval, and non-cardiac parameters such as respiratory rate, pupil diameter, and skin conductance. Increases and decreases in these patient parameters in response to changes in stimulation intensity may be used to identify the desired physiological response.

While the invention has been particularly shown and described as referenced to the embodiments thereof, those skilled in the art will understand that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope. For example, in various embodiments described above, the stimulation is applied to the vagus nerve. Alternatively, spinal cord stimulation (SCS) may be used in place of or in addition to vagus nerve stimulation for the above-described therapies. SCS may utilize stimulating electrodes implanted in the epidural space, an electrical pulse generator implanted in the lower abdominal area or gluteal region, and conducting wires coupling the stimulating electrodes to the generator. 

What is claimed is:
 1. An implantable neurostimulation system, comprising: a first VNS electrode assembly configured to couple to and deliver electrical stimulation to a vagus nerve; and a first CBS electrode assembly configured to couple to and deliver electrical stimulation to carotid baroreceptors; and a pulse generator comprising: a vagus nerve stimulation (VNS) subsystem comprising VNS stimulation circuitry; an implantable carotid baroreceptor stimulation (CBS) subsystem comprising CBS stimulation circuitry; and a control system that: activates the VNS subsystem and controls the VNS stimulation circuitry to deliver electrical energy to the first VNS electrode assembly according to a first set of parameters; and activates the CBS subsystem and controls the CBS stimulation circuitry to deliver electrical energy to the first CBS electrode assembly according to a second set of parameters different than the first set of parameters.
 2. The system according to claim 1, further comprising: a first lead assembly coupled to the pulse generation module, said first lead assembly comprising the first VNS electrode assembly and the first CBS electrode assembly.
 3. The system according to claim 2, wherein: the first lead assembly comprises a bifurcated portion coupled to a first VNS lead portion and a first CBS lead portion, wherein the first VNS electrode assembly is provided at a distal end of the first VNS lead portion and the first CBS electrode assembly is provided at a distal end of the first CBS lead portion.
 4. The system according to claim 2, wherein: the first lead assembly comprises a cuff portion configured to wrap around both the vagus nerve and a carotid artery, said first VNS electrode assembly and the first CBS electrode assembly being provided on the cuff portion.
 5. The system according to claim 1, further comprising: a first lead assembly coupled to the pulse generation module, wherein said the first VNS electrode assembly is provided at a distal end of the first lead assembly; and a second lead assembly coupled to the pulse generation module, wherein said the first CBS electrode assembly is provided at a distal end of the second lead assembly.
 6. The system according to claim 1, further comprising: a first lead assembly coupled to the pulse generation module, wherein said the first VNS electrode assembly is provided at a distal end of the first lead assembly; a second CBS electrode assembly configured to couple to and deliver electrical stimulation to carotid baroreceptors; and a second lead assembly coupled to the pulse generation module, said second lead assembly comprising a bifurcated portion coupled to a first CBS lead portion and a second CBS lead portion, wherein the first CBS electrode assembly is provided at a distal end of the first CBS lead portion and the second CBS electrode assembly is provided at a distal end of the second CBS lead portion.
 7. The system according to claim 1, further comprising: a second VNS electrode assembly configured to couple to and deliver electrical stimulation to a vagus nerve; a second CBS electrode assembly configured to couple to and deliver electrical stimulation to carotid baroreceptors; a first lead assembly coupled to the pulse generation module, said first lead assembly comprising a first bifurcated portion coupled to a first VNS lead portion and a first CBS lead portion, wherein the first VNS electrode assembly is provided at a distal end of the first VNS lead portion and the first CBS electrode assembly is provided at a distal end of the first CBS lead portion; and a second lead assembly coupled to the pulse generation module, said second lead assembly comprising a second bifurcated portion coupled to a second VNS lead portion and a second CBS lead portion, wherein the second VNS electrode assembly is provided at a distal end of the second VNS lead portion and the second CBS electrode assembly is provided at a distal end of the second CBS lead portion.
 8. The system according to claim 1, further comprising: a heart rate sensing module coupled to the control system.
 9. The system according to claim 8, wherein: the heart rate sensing module is configured to detect electrocardiographic (ECG) signals between an electrically active portion of a housing of the pulse generation module and one or more of the first VNS electrode assembly and first CBS electrode assembly.
 10. The system according to claim 1, wherein: the control system is configured to modify a stimulation parameter of the CBS subsystem in response to detected state changes.
 11. The system according to claim 10, wherein: the control system is configured to modify the stimulation parameter of the CBS subsystem during predetermined periods of time.
 12. The system according to claim 10, wherein: the control system is configured to modify the stimulation parameter of the CBS subsystem in response to detected physiological changes.
 13. The system according to claim 12, wherein: the control system is configured to modify the stimulation parameter of the CBS subsystem in response to detected changes in heart rate.
 14. The system according to claim 12, wherein: the control system is configured to increase the stimulation parameter of the CBS subsystem and increase a stimulation parameter of the VNS subsystem in response to detected physiological changes.
 15. The system according to claim 14, wherein: the control system is configured to alternately increase the stimulation parameter of the CBS subsystem and the stimulation parameter of the VNS subsystem in response to detected physiological changes.
 16. The system according to claim 14, wherein: the control system is configured to simultaneously increase the stimulation parameter of the CBS subsystem and the stimulation parameter of the VNS subsystem in response to detected physiological changes.
 17. The system according to claim 1, wherein: the control system is configured to activate the VNS subsystem to deliver electrical stimulation with a first stimulation parameter and to activate the CBS subsystem to deliver electrical stimulation with a second stimulation parameter different than the first stimulation parameter, wherein the first and second stimulation parameters correspond to one or more of the following: stimulation amplitude, stimulation frequency, stimulation pulse width, or stimulation duty cycle.
 18. The system according to claim 1, wherein the second set of parameters comprises an amplitude between 0.5 mA to 7.0 mA and a stimulation frequency between 20 Hz and 100 Hz. 